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For years, e-mail providers, IT departments, and network operators have fought spam with the help of technology that examines what messages say. Nick ­Feamster, an assistant professor at Georgia Tech, had a better idea. Instead of examining content, he looks at how messages move through networks, on the theory that the traffic flow of legitimate messages and spam should be different.

For example, Feamster found that spammers often try to hide in "dark space"--normally unconnected Internet addresses. Suddenly, a previously unreachable block of addresses would light up, send out a bunch of messages, and then disappear. Watching for phantom networks that appear for 10 minutes at a time turned out to be one way to identify and stop spam. His strategies have been adopted by companies such as Yahoo and McAfee in their ongoing struggle to prevent spam from reaching users. --Erica Naone

Global gunk: Nick Feamster's research team tracks the regions of the world most afflicted by spam.
Credit: Feamster